Electric control circuit



Sept. 18, 1945. o. w. LIVINGSTON 2,385,214

I ELECTRIC CONTROL CIRCUIT Y Original Filed April as, 1942 s Sheets-Sheet 1 Fig. 1.

Invefitor: Orr-in W Livin ston,

' His Attorheg.

Sept. 18, 1945. o. w. LIVINGSTON 2,335,214

ELECTRIC CONTROL CIRCUIT Original Filed April 23, 1942 3 Sheets-Sheet 2 Fig. 2.

Inventor: Orrin Livingston,

y a'lu (fm His Attorney Sept. 18, 1945. o. w. LIVINGSTON ELECTRIC .CONTROL CIRCUIT Original Filed April 23, 1942 '3 Sheets-Sheet 3 CONTRDL Fi. .4. m /82 gston, M

u u r m 0 P t.m o nw w eL A m s In i a 0 W m Patented Sept. 18, 1945 sLnc'raro couraoncmcvrr Orrin W. Livingston, Scotia, N. Y., assigncr to General Electric Company, a corporation oi New York Original application April 2:, 1942, Serial No. v

440,159. Divided and this application Beptemr ber 11, 1943, Serial No. 502,834

8Claims.(Ol.175--363) Y My invention relates to electric control circuits and more particularly to improved circuits for producing a periodic voltage. The present inven: tion is particularly well adapted for use in connection with control systems for resistance welders.

This application is a division of my application Serial No. 440,159, filed April 23, 1942, entitled Electric control circuit, and now United States Letters Patent 2,348,553 granted May 9, 1944.

Electric valve circuits for energizing the welding transformer of resistance welding systems have been widely used and in many of these systems it is desirable to provide a periodic or timing voltage. In accordance with the present invention there is provided an improved circuit for producing a periodic voltage. which may be readily modified in accordance with the operation of a timer, a heat control circuit, or some condition of the load circuit. such as the power factor, to modifyv the periodic voltage. I

It is an object of my invention to provide a new and improved electric controlcircuit.

It is another object of my invention to provide a new and improved electric control circuit for producing a periodic control voltage;

It is a still further object of my invention to provide a new and improved electric control circuit for producing aperiodic voltage in which means are provided for modifying the periodic voltage in accordance with one or more condi-' tions.

In'accordance with the illustrated embodiments of my invention, I provide an improved control circuit which is utilized as a frequency determining circuit for a frequency changer, The frequency changer comprises two groups of electric valves arranged to conduct alternately and interconnecting a polyphase supply circuit with a single phase load circuit. Current'of one polarity is supplied to the load circuit through the valves of one group conducting in succession, and current of the opposite polarity is supplied through the valves of the other group conducting in succession. The frequency established by the frequency determining circuit may readily be adjusted and is synchronized with the alternating current supply circuit to maintain the desired wave shape of the low frequency voltage.

The operation of the frequency determining circuit. of the electric valve frequency changer is tronic circuits are synchronized withthe low frequency voltage by means responsive to the frequency established by the frequency determining circuit of the electric valve frequency changer. Means for delaying'thetransfer of current from one group of valves of the electric valve frequency changer to the other beyond the time established by the frequency determining circuit are provided to permit the flow of lagging poweriactor current. Thus, the illustrated embodiment of the invention provides for intermittent energization of a single phase low frequency load circuit from a polyphase alternating current circuit of higher frequency in which transients are eliminated and a considerably better loading of the Suppl-V.

cuitis'obtained. My invention will be better understood by reference to the following description taken in connection with the accompanying drawings and its modified by electronic timing circuits which are utilized to determine the periods at which the frequency changer is operative and inoperative to transfer energy to the load circuit. These elecscope will be pointed out in the appended claims. In the drawings. 8. lis a schematic representation of one embodiment of my invention; Fig. 2 is a schematic representation of a modification; Fla. 3 is a schematic representation of another embodiment of my inventionwhich incorporates additional features of control in a circuit similar to the modification of Fig. 1; and Fig. 4 is a. de-

, tailed viewof one of the transformers utilized in the arrangement of Fla; 8. I Referring now to Fig. l of the drawings,1have shown my invention embodied in an electric valve translating system and a control circuit therefor for effecting the'intermittent energization of a load circuit ill with current of one frequency from an alternating current supply circuit ll of another frequency. As illustrated, the load circult is the worl: circuit of a resistance welder and is energized by the secondary winding ll of a welding transformer ll having a midtapped primary winding II. The end terminalsofthe primary winding 14 are connected respectively with the neutral terminals of the Y-connected secondary windings l5 and ii of a supply transformer ll, having the primary winding ll thereof energized from the alternating current supply circuit ii. The midtap of the transformer winding 14 and the phase terminals of the transformer secondary windings l5 and it are interconnected by groups of electric discharge valves I9, 20, 2i and 22, 23, 24. The electric valves may be of any of the types well known in the art and, as illustrated, each comprises an envelope containing an ionizable medium such as a gas or vapor, and enclosing an anode 25, a cathode 26, an associated heater element 21 and a control 2 2,sao,a14

member or grid II. As shown in the drawings. the anodes of valves It, It and ii comprising one group are connected with the phase terminals of secondary winding II and the anodes of valves 2:, 23 and 24 comprising the other groupare connected with the phase terminals of secondary winding it. The cathodes of the group comprising valves ll, II, II are connected togetllr by conductor It and the cathodes of the group comprising valves 2!, 2i and II are connected together by conductors II. The catbodu of the two groups are connected tocether through the midtapped primary winding ll of a current transformer 3!. The circuit to the primary winding I4 M of the welding transformer I2 is completed from W the midtap of winding II to midtap of winding N by conductor 33. The secondary winding 84 of the current transformer II is provided for a control function to be described at a later point in the specification Asiswellunderstoodbytlmeeskilledintbeart. the power circuit thus far described may be controlled so that the groups of valves ll, 2., II and 2!, 21, 2|, conduct alternately, with the valves of each group conducting consecutively and in this way to supply alternating current to the load circuit having a lower irequency than the supply circuit. It will also be understood that the voltage supplied to the load circuit may be controlled by adjusting the phase shifting means. In awelding circuit this provides means for controlling the welding heat. In order to control the moment in the voltage wave of the alternating current supply circuit II that each of the valves is rendered conductive, I provide an excitation circuit including means for impressing an alternating component of voltage 0! the frequency of the supply circuit on the control members 28. In order to control the transfer of current irom one group of valves l8, 2|, H to the other group 21, II, It and back again at a definite periodicity I provide for producing a second component oi control voltage which, in the arrangement iihistrated, is a direct current component. This component voltage is also modified to render all of the electric valves non-conductive to determine the periods during which the load circuit is not energilcd. The alternating current component of excitation voltage is derived from the alternating current supply circuit Ii and impressed on the control members It by the phase terminals of the Y- connected secondary windings It and I. of excitation transformer 31 having the delta-connected primary winding I. thereof energised from a phase shifting device I! which in turn is energized from the alternating current supply circuit ii. The hase terminals of the secondary windings 35 and it are connected respectively with the control members II of electric valve I844 through suitable current limiting resistors ll. The control member-to-cathode circuit of electric valves It, It and ii is completed from the neutral terminal ll of secondary winding 3! of the excitation transformer through conductor 42, resistor 43, resistor 44, the left-hand portion of resistor 45, a portion of a voltage dividing resistor 46, conductor ll, hall. the primary winding 3| 0! current transformer 32, to the cathode conductor 29 of the electric valves ll, 20, 2|. In a similar manner the control member-to-cathode circuit of the electric valves 12, 23 and 24 is completed from the neutral terminal M of the secondary winding 36 of the excitation transformer through a conductor l9, resistor 50, resistor ii, the right-hand portion of the resistor 45, a portion of the voltage dividing resistor It. conductor 41, hair the primary winding ii of transformer 32. to conductor a.

From the ioregoing description, it is apparent that the excitation circuit of valves II, II, ii includes inseriesresistorell, ,apartoi'reeistor II and a portion 01 voltage dividing resistor l. and likewise that the excitation circuit of valves l2, N, N includes in series resistors II. II, a part of resistor it and aportionoivoltagedividiriresisior 4. In accordance with important 10lamres of the present invention, the voltalee acrul close resistors are controlled to determine the frequency and the periods or energiaation and deenergixation of the load circuit as well as to permitlaggingpowercurrenttoiicwtotheweldins circuit. A source oi direct current control voltase forenergisingtheeeredstoreilimpremedoncmdoctors I! and I. In the arrangement illustrated in the drawing the direct current is obtained ircmonephaseofthealternatingcurrentmpply circuit ii bymeansolafullwaverectiiierincludingatransformerllaandanelectricvaivemeane llhavingtwodiachargepatbs. Tbeoutputoi u the electric valve rectifier system including trans.

former "a and valve means 4 is filtered by inductive reactances'landl'oonnectedinmries withoneofthedirectcurrentlineeandcapacitcrl Slandtlconnectedinparallelwiththedirect 'currentoutputcimntoltheeiectricvalverectiiier.

InorderthattbeebctncvaIvesystemJncIuding the groups'o! valves il, a, ii and II, a, ll, operate as a frequency changer it is necessary tomndercneofthegroupenonconductiveforaperiodeqimltoonehalf-cycleoi thefrequencyoithe'loadcircuit. Intheilluetrated embodiment of the invention this is accompliahedbymeansoranelectrontcoeciilator andepecincallyanelectricvalveinverterottbe paralleltypehavingtbevalveeconnectedwith respect to the source ol direct current control voltage and the resistor-sin the excitation circuit 0! the groups or valves is, a, ii and 22, It, It

alternately to impress a negative voltage in the neutral connection of the excitation transformer secondaries ll and 30, respectively, at the frequency 0! operation of the inverter.

Referring now to the drawing the inverter comprises electric discharge valves I. and I preferably of the type employing an ionizable medium, such as a gas or vapor, and each comprising an anode ii, a cathode l2 and a control member or grid '8. The cathodes of valves It and I are connected together by a conductor N and to the negative side of the direct current control voltage supply I through a resistor 08. A resistor Old is connected in series with resistor 48 and the two connected across the direct current 00 lines l2, 3. The anode Ii or valve II is con- 5 connected with the positive side of the direct current control voltage 2 it will be seen that this circuit provides a parallel inverter energised from the source '2, $3 in which the anode circuit of one of the discharge paths of the inverter includes resistor 44 and hall! of resistor I which are also in the neutral connection or the excitation transformer secondary winding ll associated with the group of electric valves It, 2', 2 I, while the anodecathode circuit of the other discharge path or the parallel inverter includes the resistance element li and the righthandportion of resistance element ll whichare also in series in the neutral connection of the excitation transformer secondalfy'winding ll associated with valves 22, ll, II.

From an inspection of the circuit Just described, it

is apparent that when valve It is conducting the terminal It will be brought to substantially the voltageof conductor 04 which is negative with respect to conductor 52 and in this way a negative bias is impressed on the neutral of transformer secondary winding Si by resistor 44 and a portion of resistor 4'. This bias has a magnitude sufncient to overcome the positive bias inserted in the circuit by the voltage divider u and the periodic voltage of winding I! and thereby render the group of valves II, II. 'II nonconducting. when the valve a is rendered conductive the a terminal '1 is brought to substantially the poten- I circuit is associated with each of the control members l! of valves It and II and a commutating condenser CI isconnected between the terminals through a circuit including resistor ll, resistor 18, a portion of voltage dividing resistor H. and the anode-cathode circuit of electric valve ll so that after a predetermined time the control member or valve it will again be rendered more positive than the critical voltage and with the aid of commutating condenser 88 current will be commutated from valve so to valve II. From the above description it is seen that the frequency of operation of the inverter is controlled by the constants of the discharge circuits for the capacitors I. and It. B making the constants of these two circuits equal the periods of conduction of valves I. and II are equal and the electric valve frequency changer-including thegroups of valves II. II, Ii and 22, It, It operates to produce successive half cycles of equal duration.

While the resistance capacitance timing oi the inverter may be made relatively accurate, I provide means for synchronizing the operation of the inverter with the voltage of-the alternating cur rent supply circuit ii in order to prevent drifting of the inverter with respect to the alternating current supply circuit II and inthis way main- I and U to render the anode of one of the valves negative momentarily at the time that the control member of the other valve is energized to render the associated valve conducting. The control member 68 of electric valve II is connected to the in series with resistor it across direct current source l2, ll. Similarly. a circuit from the control member I of the valve I. is completed to the conductor 04 through a resistor ll and a portion -0! the voltage dividing resistor 14.

The operation of the condenser resistor circuit for determining the frequency of operation of the inverter comprising electric valves I! and I will now be briefly described. Assuming that valve 59 has started to conduct, currentwill flow from the terminal 01 through condenser I, resistor I0, through the control member to the cathode chcult to the negative line of the direct current control voltage source. This charges the condenser ll so that the terminal thereof electrically nearer the control member of the valve 58 is more negative. During the time that valve 89 is conducting the condenser ll discharges through a circuit including the anode-cathode circuit of valve 50, conductor 84, a portion of voltage dividing resistor 14, resistor 15 and resistor 12. The time required for-the condenser H to discharge sufficiently to renderthe control member '8 of valve 80 more positive than the critical voltage may be adjusted by varying the position of the slider on the voltage dividing resistor ll. At the time the control member of valve 0 becomes more positive than the critical voltage, current is transferred from valve 80 to valve 00. with the aid of the commutating capacitor 68 which has been charged during the conducting period ofvalve- I! to render the anode thereof temporarily negative. When the valve 10 is conducting and condenser ll is 1 charged so that the control member of valve is rendered negative condenser I! is discharging tain the desired wave shape of voltage on the load circuit. In the arrangement illustrated this means for synchronizing the operation of the inverter comprises means for impressing period'c voltages of peaked wave form on resistors IO and 12 associated with the control members I of valves I! and 60, respectively. The synchronizing voltages are obtained from a network of resistors. capacitors and cold cathode discharge devices of the type commonly referred to as glow tubes.

Referring to the drawings. resistors It, 11, and I8 and capacitors ll, 00. and I are connected to provide a three-phase Y-connected network with each phase including in series a resistor and a capacitor. One terminal of each of the capacitors IO, and ti are connected together to provide a neutral terminal H, the voltage of which with respect to the output of the phase sh fting device 39 is established by Y-connected imped ance elements such as resistors "a. The discharge devices 83 are connected in a three-phase Y having one electrode of each device connected to a neutral connection "a and the other terminal of each device connected respectively to the common terminal of the res'stor and capacitor of each of the phases of the Y-connected networkof series resistors and capacitors. Connected across the neutral terminals 82 and Ila are the primary windings l4 and 85 of transformer devices 86 and 81, respectively. Secondary winding 88 of transformer II is connected across the lesistor 10 in circuit with the control member .8 of electric, valve 59. A capacitor 09 igconnected in series-with the secondary to other high impedance to the flow of direct current through the transformer secondary winding 88. Similarly, the secondary winding 90 of transformer 81 is connected across the resistor 12 of electric valve 60 and a capacitor 9| is connected in series therewith to offer a high impedance to the flow of direct current through the transformer winding. From the drawings it is seen that this network provides three parallel circuits across the terminals of the primary windings 84 and 85 with each circuit including in series a glow tube and capacitor. The breakdown of any glow tube permits the flow of current through the transformer primary winding. The-capacitors I9, an and 8| ,are charged from the alternating current supply circuit II through resistances 18, ll and II, respectively. and when any one of the capacitors has charged to a voltage corresponding to the breakdown voltage of the associated glow tube a voltage is suddenly impressed on the transformer windings which is equal to the difference between the breakdown voltage and the voltage of conduction of the glow tube. The condenser resistor circuit and the characteristics of the glow tube are so correlated that the glow tube breaks down at a predetervmined point in each half cycle of voltage in the alternating current supply circuit II. While it is possible to adjust the instant of breakdown of device 83, by varying the magnitude of resistors 16, 11, I8 or capacitors I9, 80, BI, it has been found desirable to energize the network from the supply circuit II through phase shifter 39 which also energizes transformer 37. Thus it is apparent that one of the glow tubes breaks down every sixty electrical degrees with respect to the voltage of the alternating current circuit I I and that voltage peaks are produced in transformers 85 and 81 every sixty electrical degrees. The secondary windings 88 and 90 are connected with resistors and 12, respectively, so that the peaks impressed on the control members of electric valves 59 and 50 at any instant are of opposite polarity. Circuits for producing voltages of peaked wave form and adjustable phase of the type described forms the subject matter of my application Serial No. 440,157, filed April 23, 1942, now United States Letters Patent 2,366,537 granted January 2, 1945,

and assigned to the same assignee as the present invention. As applied to the system of the present invention these peaked voltages are utilized to synchronize the operation of the inverter comprising valves 59 and 60 with the alternat ng current supply circuit II. This is accomplished by correlating the magnitude of the voltage peaks with the voltage impressed on the control members 63 of valves 59 and 50 by condensers 69 and TI so that the resultant voltage exceeds the critical voltage at the desired instant.

From the standpoint of symmetrical wave shape in the load circuit it has been found desirable to operate the frequency changer-so that the load frequency where Fe is the frequency of the supply, N is an integer and P is the number of phases of each of the supply transformer secondaries. If Fe sixty cycles, N is two, and P is three as it is in the illustrated embodiment, FL. is /1 cycles. One half cycle of the load frequency then extends over a period of 420 electrical degrees with respect to a sixty cycle base. When operating on this basis it is desired that current be transferred from tube 59 to tube 60, or vice versa, every 420 electrical degrees. Since the peaked voltages impressed on resistors I0 and I2 occur every sixty electrical degrees it is necessary for synchronous operation to choose the circuit constants of the elements in circuit with control members 63 so that the voltage of the control member of the tube which is to be rendered conductive comes near enough to the critical voltage at the end of the 420 degree interval that the voltage of peaked wave form is sufficient in magnitude to render the valve conductive.

The system thus far described provides for the transformation of alternating current voltage of the frequency of the supply circuit II to voltage of another frequency which is impressed on the transformer 13, the frequency being determined by the inverter comprising tubes 59 and 60 and the load voltage being synchronized with the supply circuit II by means of peaked voltages impressed on the control members of valves 59 and 60 by transformers 00 and 01.

My invention is particularly well adapted for effecting the intermittent energization of the load circuit and also providing for the flow of lagging power factor current. The features of control which provide this operation will now be described. Energized from the direct current lines, 52, 53 is a parallel type electric valve inverter comprising electric valves 82 and 93. These electric valves are preferably similar to the valves 59 and 60 and each comprises an envelope containing an ionizable medium such as gas or vapor, an anode 94, a cathode 95, a control member or grid 96, and a shield grid 01. The cathodes 95 of valves 92 and II are connected together by a cathode bus 00 and through series resistors 09 and I00 to the negative line 53 of the direct current control voltage source. The anode of electric valve 92 is connected with the positive line 53 through a resistor IN. The anode of electric valve 03 is connected with the positive line 02 of the direct current control voltage source through resistors I02 and I03 in series. A commutating capacitor III is connected between the anodes of valves 02 and 93. The control member 96 of valve 02 is connected to'an intermediate point on resistor I03 through resistor I00 and capacitor I06 and also to the cathode bus through a resistor I", the secondary winding I00 of a synchronizing transformer I00. The cathode-to-control member circuit of the electric valve 03 is completed through the resistor 0!, which impresses a negative bias on the control member, the secondary winding III of a transformer III and a current limiting resistor II2. The primary winding III of the transformer III is connected in the anode-cathode circuit of an electric valve I which is of the same construction as the electric valves 02 and 03 and comprises an anode III, a cathode Iii, a control member or grid I I1, and a shieldgrid III. One terminal of the transformer primary winding H3 is connected to the positive terminal 02 of the direct current control voltage source and the other terminal thereof is connected to the anode II! of valve Ill. The cathode III is connected to one of a pair of spaced fixed contacts III of an electromagnetic switch I20. A condenser III has one electrode thereof connected with the terminal 02 of the direct current circuit and the other treminai thereof connected to the other fixed contact Ill. The switch I2. is also provided with spaced fixed contacts I22 and a movable bridging contact I23 controlled by an operating coil I24 which is energized from one phase of the source II'under the control of a manual switch I25. One of the fixed contacts I22 is connected to the cathode bus 00 through a resistor I20 while the other of the fixed contacts I22 is connected to the same terminal of condenser I2I as one of the fixed contacts H0. The bridging contact I2! is arranged to connect the contacts I22 when the operating coil I24 is deenergized and in this way complete a charging circuit for condenser Hi from the positive line 02 of the direct current circuit through resistors I26, 99 and I00 to the negative line 53 of the direct current circuit. With electric valve 92 conducting this charge is limited to the drop across electric valve 92 and resistor IOI. When the coil I24 of switch I20 is energized the contacts H9 are bridged and the condenser is discharged through the electric valve II5. shunting the contacts H9 and I22 of the switch I20 is a series connected manual switch I21 and a variable resistor I28. The circuit for energizing control member II! of electric valve H4 is completed through contacts II9 of switch I20, condenser I2I, resistor IIII, electric valve 92, resistor 99, the secondary winding I29 of a synchronizing transformer I30, and a current limiting resistor I3I The synchronizing transformers I09 and I30 are utilized to produce synchronizing voltage impulses at the frequency supplied to the load circuit, or in other words at the frequency of operation of the inverter comprising electric valves 59 and 90. The circuits employed for obtaining the peaked voltages are similar to those used for synchronizing the operation of the inverter with the supply circuit. As illustrated, the primary winding I32 of transformer I30 is connected in series with the glow discharge device I32a and across a condenser I33 which is charged in accordance with the voltage across commutating capacitor 09 through an adjustable resistor I34. Similarly, the primary winding I99 of synchronizing transformer I09 is connected in series with a glow discharge device I30 and across a condenser I31 which is charged in accordance with the voltage of commutating capacitor 99 through an adjustable resistor I30.

The electric valves 92, 93 and H4 and their associated control circuits provide an electronictimer control which operates to chest intermittent energization of the load circuit with trains of half waves of voltage having the frequency established by the electric valve inverter comprising valves 99 and by controlling the conductivities of-electric valves I39 and I40. These latter valves are preferably of the high vacuum type and each comprises an anode III, a cathode I42 and a control member or grid I49. The cathodes of both valves I39 and I40 are connected to the same cathode bus 94 as valves 99 and 90. The anode III of valve I39 is connected to terminal 33 through a resistor 43 while the anode III of valve I40 is connected with the terminal 91 through resistor 90. Thus, if electric valve I39 is conducting it maintains the group of valves I9, 29 and 2I nonconducting by maintaining a negative voltage across resistors 43, 44 and a portion of resistor 45 in the same manner that conductlon of valve 59 maintains the terminal 00 at a negative potential. Similarly, when valve I40 is conducting the group of valves 22, 23, 24 is rendered nonconductive. In this way by controlling the conductivity of valves I39 and I40 it is possible to delay the transfer of current from the valves I9, 20, H to the other group 22, 23, 24, for example, beyond that determined by operation of electric valves 59 and 00 and by simultaneously controlling the conductivity of valves I39 and I40 in the same way to cause intermittent energize.- tIon of the load circuit. T0 effect the desired control of the electric valves I39 and I40 the control members thereof are energized in accordance with the conductivity of electric valves 92 and 93 and also in accordance with the flow of current through the respective groups of valves I9, 20, 2I and 22, 23, 24. For example, the control member I43 of electric valve I39 connected through current limiting resistor I44 to one end terminal of the secondary winding 34 of current transformer 32 while the control member I49 of electric valve I40 is connected through a current limiting resistor I45 to the other end terminal of the secondary winding 34. The mid terminal of the secondary winding 34 is connected to the anode of electric valve 93. Thus when electric valve 93 is conducting the control member to cathode circuit of electric valves I39 and I40 is completed through valve 93, cathode bus 98, resistors 99, I00 and 05. When valve 93 is nonconducting and valve 92 is conducting the circuit is completed from the midpoint of transformer secondary winding 34 through resistors I03, I02, IIlI, electric valve 92 and resistors 99, I00 and 65. By proper P p n ng of the resistors enumerated above it is possible to render the electric valves I39 and I40 conducting to a. substantial degree when electric valve 92 is conducting, since at that time the midpoint of the transformer 34 is raised substantially to the full positive voltage of the line 52. When electric valve 93 is conducting, the midpoint of transformer winding 34 is depressed substantially to the voltage of one terminal of resistor 99 which is sufliciently negative to bias the electric valves I39 and I40 substantially to cutoff. It is understood that the proper values of bias under the different conditions of conductivity of valves 92 and 93 is obtained by proper proportioning of the resistance elements'enumerated in the circuits of the control members I43 of electric valves I39 and I40. In the above discussion the effect of any voltage appearing across the opposite halves of the winding 34 has been neglected. This transformer is included in the control member circuit of the electric valve I34 to provide a source of bias on the control members dependent upon the flow of current in either group of valves. For example, if current is flowing through the group of valves I9, 20, 2I it is desirable that the valves 22, 23, 24 be held off even though the master inverter operates to render the group of valves 22, 23, 24 conductive. The end terminals of the secondary winding 34 are connected to the control members of valves I39 and I40 in such a manner that the voltage impressed on the control member of electric valve I40 is positive when valves I9, 20, and 2| are conducting and in this way the valves 22, 23, 24 are prevented from becoming conductive until the current conducted by valves I9, 20, 2| has ceased to flow. This provision takes care of lagging power factor current as long as the power factor does-not become so low as to extend the current for more than degrees referred to the supply line frequency after the last valve of the conducting group is rendered conductive. In the arrangement illustrated in Fig. 3 which will be described at a later point in the specification, provision is made for supplying inverter excitation with respect to the frequency of the supply line voltage so that energy may be transferred between the supply and load circuits under any power factor condition. A voltage maintaining glow discharge device I46 is connected across the transformer secondary winding 34 to maintain a substantially square voltage wave and permits a step-up transformer to be used so that substantially full controlling influence of the transformer 32 is available so long as any current whatever flows in the load circuit.

Although the operation of some parts of the circuit hasbeen included in the foregoing description, a more complete description of the operation of the system as a whole will serve to bring out more clearly the features and advantages of the present invention. Let it be assumed that switches I25 and I21 are in the open position and will value W conduct alternately at a frequency dependent upon the resistor capaciior constants of control circuits associated therewith, as previously described. However, the conduction by electric valve 22 serves to render conductive i c v ves it! and ill, which valves, so that a negativc or hold-oil voltage inrn'essed upon the neutral terminals 46 and 43, respectively, of the groups oi valvcg iii, 2%, 2i and i2, 2!, N. If it is ales ed to init te a weld; the switch I is closed. Tins closes c ill contacts H! and completes a circu the anodewathode of electric valve H4. Gondcnser iii has he the med ccmtact are closed it tends to valve iii and innaiormer winding HI.

induced in the the F53 d cod in winding 6 S. 'rrg'imgn m i in -iich till:

occ n diatom foliowing to the operascon of and tho condenser f nc ion very similar czniected series i the valves or the valve starts member-to-cathode circuit of electric valves I" and I are proportioned so that with electric valve 18 conducting the valves I" and Ill are biased substantially to cut-oil and the groups of valve i9, 20, 2| and 22, 23, 24 are rendered alternately conductive and nonconductive at the irequcncy determined by the master inverter comprising electric valve ll and I. While electric valve OI is conducting the charge on condenser l" is decreasing and alter a predetermined time depending upon the position of the slider on resistor ill and the magnitude of the capacitor Ill and resistors Ill and Ill, control member ll of valve 82 becomes sumciently positive so that a voltage impulse in the secondary winding I" of the synchronizing transformer I" is sufficient to render valve 22 conductive. At this time current is commutated from the valve I to 92 and both of the restraining valves Ill and I are again rendered conductive. In this way the load is de energized after a time interval dependent upon the period that valve 82 is nonconductive which may be adjusted by adjusting the timing circuit associated with the control member thereof. A system employing a timing circuit similar to that comprising parallel connected electric valves 02- and 83 for effecting the intermittent energization of a load circuit through controlled electric valves is described and claimed in my copending appllcation Serial No. 432,901, filed February 28, 1942, entitled "Electric valve control circuit," now United States Letters Patent 2,368,038 granted December 26, 1944, and assigned to the same assignee as the present invention. Claims covering the subject matter generic to my above identified application and the present application are pre-- sented in the earlier filed application. Deenergization or the load is also synchronized with the low frequency by means of the voltage impulse produced by winding I" so that complete cycles of the low frequency are supplied to the load circuit. Thus closing switch I" initiates a period of energization of the load circuit at the low trequency with both beginning and ending of theperiod oi energization being synchronized withthe load frequency. If it is desired to seam weld or, in other words, to produce a succession of alternate periods of energlzation and deenergizatlon of the welding circuit the switch I21 is closed; then when switch i2! is closed, electric valve H4, condenser I2! and the charging circuit therefor operate as a single tube inverter which produces a periodic impulse in the secondary winding Ill and thereby periodically render electric valve 08 conductive to initiate periodic energizatlon of the load circuit. As described before, the synchronising transformer HI synchronizes the conducting periods or electric valve I" with the load frequency. The slider on resistance 12! provides means for adjusting the interval between successive welds, or in other words the periods of deenergizatlon oi the load circuit. As described earlier in the specification the current tIIJII,

iormer 32 operates to delay the transfer or current from one group of valves to the other by rendering the restraining valve associated with the in: coming group conductive until the current conducted by the outgoing group has decreased substantially to zero. v

The magnitude of the voltage impressed on the load circuit, and in the case of a welding circuit the heat, may be adjusted by shifting the phase or the hold-oi! or restraining voltage with respect to the load circuit, as will be explained in conneclion with Fig. 3, or as illustrated in Fig. 1, may

be controlled by shifting the phase of the excitation potential at the supply frequency by means of phase shifting device 20. This provides means for controlling the magnitude of the load circuit current.

In Fig. 2 I have shown a modification of my invention which is quite similar to that illustrated in Fig. 1 and the same reference numerals have been applied to designate corresponding parts. In the arrangement shown in Fig. 2 the network for synchronizing the operation of the master inverter or frequency determining means if slightly different and the control function of electric valve II of the arrangement illustrated in Fig. 1 has been incorporated directly in the control memberto-cathode circuit of electric valve 02.

Referring now to Fig. 2 the master inverter comprising valves 09 and I is synchronized with the supply line voltage by a network I41 comprising a delta-connected primary network I including in each phase a. series connected re-' sistor I and capacitor I00. Across the capacitor in each phase is connected in series a glow discharge device IIII and a transformer primary winding I I2. Inductively coupled with the transformer winding I52 is a six-phase star connected secondary network I" having alternate phase terminals connected to the control member 02 of electric valves 58 and 00, respectively, through current limiting resistor I". The neutral of each star-connected network I" is connected to the cathode bus 84 through a conductor I. It will be apparent to those skilled in the art that the operation of the synchronizing circuit just described is essentially the same as the synchronizing network utilized in connection with the modification shown in Fig. l.

The electric valves 22 and 02 are connected In a manner similar to that shown in the modification described in Fig. l. The condenser-resistor timing circuit for the valve 00 differs from that shown in Fig. l in that one terminal of condenser I00 is connected directly with the anode of tube 92. However, the adjustment for the condenserresistor circuit is provided by means of a variable tap on a resistor I" which is connected between the cathode bus 02 and positive line 02 of the direct current supply circuit. As previously stated, the control function of the valve Ill of Fig. 1 is at least partially incorporated directly in the control member-to-cathode circuit of valve 93. Thus the control member-to-cathode circuit of valve 92 is completed through current limiting resistor II I, synchronizing transformer secondary winding I28, resistor I" to the negative side I! of the direct current supply circuit 02 which is connected with the cathode of valve 92 through resistors and I00. Movable contact I22 of switch I20 bridges fixed contacts I22 when the switch s in the deenergized position and establishes a charging circuit for a condenser III through a resistor I". The condenser III is charged by the voltage appearing across resistor I00. when switch I2! is in closed position contact I20 moves into engagement with contact I I0 and the voltage of the condenser is impressed across resistor I01 in the control member-tocathode circuit of electric valve 93.

When switch I2! is in the open position condenser I58 is charged with the right-hand plate thereof, as illustrated in the drawings, having a positive potential. When switch I25 is closed this voltage is impressed across resistor I51 so that as soon as a synchronizing impulse is induced in transformer I29 the valve 83 is rendered conductive and a period of energization of the load circuit is initiated. Except for the above differences the operation of-the modification illustrated in Fig. 2 is substantially the same as the operation of the modification of Fig. l and will not be repeated.

In the arrangements thus far described no provision has been made for the transfer of lagging power factor current where the angle of lag is more than 180 degrees referred to the frequency of the supply circuit. Also, in these arrangements control of load circuit voltage has been effected by means of a phase shifting device for shifting the phase of the excitation applied to the main electric valves at the frequency of the supply circuit. It is contemplated. according to the present invention, that the voltage of the load circuit be controlled by shifting the low frequency excitation of the frequency changer or, in other words, to delay the transfer of current from one group of valves to the other to control the efi'ective voltage applied the load circuit and also to provide for effecting the transfer of energy at any power factor. These two features have been incorporated in the modification shown in Fig. 3. This modification is in general similar to the arrangement of Fig. 'l and the same reference numerals have been applied to corresponding parts.

Referring now to Fig. 3 of the drawings, means I for delaying the transfer of current from one group of main electric valves to the other beyond the point which would be established by the restraining valves I 00 and I40 and the control circuits associated therewith are provided by additional electric valve means Ill and I6I connected respectively in parallel with electric valves I20 and I. These valves, like valves I" and I40 are preferably of the high vacuum type and each comprises an anode I02, a cathode I63 and a control member or grid I". In order to delay the transfer of current from one group of valves I9, 20, II to the other group of valves 22, 20, 24 beyond the time established by the master inverter or frequency determining circuit comprising electric valves 0! and 00, the restraining valves I and IN are controlled in accordance with the current conducted by the two groups of electric valves by means of a circuit designated generally by the numeral I", and comprising means for producing a voltage which lags the current in transformer H by an adjustable amount. As illustrated in the drawings, the substantially square shaped voltage appearing across glow discharge device I which is in phase with the current in transformer 32 is impressed on the primary winding of an insulating transformer I" having a rnidtapped secondary winding I01. The

' midtap is connected with the midtap of transformer winding 24 and to a conductor I" which is periodically brought to a negative potential byoperation of the timer control I" which has been illustrated schematically in Fig. 3 and may for example comprise electric valves 02, II and Ill and associated circuits as illustrated in Fig. l and described at an earlier point in this specification. The secondary winding I61 is connected to energize a glow discharge device I10. As illustrated, each end terminal of the transformer winding 1 is connected to one terminal of the discharge device I10 through a variable resistor III and a reactor I12. The variable resistors III are connected together so that they may be varied simultaneously. As is well understood in the art, this circuit will impress a voltage on the glow dis-. charge device I10 which lags the voltage across discharge device I46 by an amount dependent upon the setting of the variable resistors IN. The control members I84 of electric valves I60 and Iii are connected respectively with the opposite terminals of the glOW discharge device I10 in such a manner that the instantaneous polarity of the voltage impressed on the control members renders the restraining valves I10 and HI selectively conductive to delay the transfer of current from one group of valves I9, 20, 2I to the other group of valves 22, 23, 28 beyond that which would normally be established by the master inverter comprising electric valves 59 and E0. The man ner in which valves I50 and IGI function to delay the transfer of current from one group of main electric valves to the other will readily be understood i'rom the description of operation of valves I39 and I80. In this way the transfer of current from one group of valves to the other is delayed in accordance with the setting of the variable resistors Ill and is effective to vary the magnitude of the voltage impressed on the load circuit, or in other words. to vary the welding heat.

In order to control the transfer of energy between the supply and load circuit at a power factor causing current to tend to flow for more than 180 degrees referred to thesupply circuit after the master inverter has operated to effect transfer current to the other group of main electric valves, it is necessary to render the electric valves successively conductive at the frequency of the supply circuit and at a sufficient time before the impressed anode voltage becomes negative to allow for commutation. That is, it is necessary to supply inverter excitation to the electric valves with respect to the supply circuit In accordance with the illustrated embodimerit I provide means for supplying peaked excitation in the proper phase relation with respect to the supply circuit for exciting the electric valves for inverter operation by means of a plurality of the transformers I13 to I18 inclusive, each having a primary winding I15 energized from the proper phase of a three phase supply I88 which, as illustrated, is derived from the supply circuit I I through a phase shifting device IBI. In Fig. 4 I have shown schematically the construction of one of the peaking transformers and as illustrated it comprises in addition to the primary winding I19, a secondary winding I82 and a midtapped tertiary or control winding I83. The windings are wound on a core I88 which is provided with a saturable leg I85 and a shunt I88. Windings I82 and I83 are mutually closely coupled and loosely coupled with winding I19.

Referring to Fig. 3, the secondary windings I82 of the transformers I13 to I18 inclusive, are connected respectively in circuit with the control members 28 of the electric valves I9 to 28.. The selective application and removal of the voltage peaks furnishing the inverter excitation for the two groups of main electric valves I9, 20, 2I and E2, 23, 28 is effected by periodically short circuiting certain of the tertiary windings I83.

as illustrated in the drawings, means for selectively short circuiting these tertiary windings I83 is provided by the electric valves I81 t I92. Each of the valves is constructed to operate as a full wave rectifier and is connected so that when it is conducting it short circuits both halves of one or the control windings I83. The cathodes or all of the electric valves I81 to I92 are connected together and the direct current circuit of the parallel connected recthiers comprising windings I83 and electric valves I81 to I92 is short circuit/ed. The cathode bus I93 of these rectifier-s is connected to the midpoint of transformer winding 38 through a suitable biasing means such as a battery I98. The circuit of the control member of electric valves I81, I88 and I89 is completed from an end terminal of the transformer winding 88 through a current limiting resistor, while the control member circuit for the valves I88, I8I, I82 is completed from the opposite terminal of transi'ormer winding 38 through a current limiting resistor. Thus, the cathode to control member circuit of each group of valves I81, I88, I88 and ISO, I9I, I92 includes a source of positive bias in the form of battery I98 and a bias potential depending upon the current flowing in the transformer winding 38 which, as previously explained, is dependent upon which group of main electric valves is conducting current. Battery I88 supplies a positive bias of sutlicient magnitude to render the valves I81 to I82 conductive when no current flows in the winding 88. When either group of main electric valves conducts current the potential of one terminal of winding 88 is instantaneously positive and the other terminal is negative. The transformer 32 preferably steps the voltage up to such an extent that as soon as appreciable current flows in the primary winding 3| thereof the secondary voltage reaches the breakdown voltage of the discharge device I88 which maintains the bias voltage supplied by the transformer winding 88 constant substantially throughout the variations of load current, This voltage is or a magnitude suflicient to overcome the positive bias of battery I98 and render nonconductive the group of valves controlled by the terminal of transformer winding 88 which is instantaneously negative. This open circuits the windings I88 and renders one group of transformers such as I18, I18, and I18 effective to supply inverter excitation to the main electric valves I8, 28, 2|. As soon as the current conducted by this group oi main electric valves is reduced to zero corresponding valves I81, I88, I89 are rendered conductive by bias battery I88 and the inverter excitation supplied by secondary windings I82 is removed from these main valves. Similarly, when valves 22, 28, 28 conduct the valves I80, I8I, I92 are rendered nonconductlve and inverter excitation is supplied to the main electric valves 22, 23, and 28 by means or the secondary windings I82 associated with transformers I18, I11, and I81. The magnitude of the voltage peaks impressed on the control members of the electric valves I8, 28, 2| and 22, 28, 28 by means of the secondary windings I82 is sufficient in magnitude to excite the valve for-inverter operation Independently ofthe operation of the master inverter comprising electric valves 88 and 60. Thus I provIde an arrangement which selectively supplies inverter excitation to the different groups or main electric valves in accordance with current flowing in the load circuit.

While I have shown and described particular embodiments of my Invention, it will occur to those skilled in the art that various changes and modifications may be made without departing from my invention, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a source 01' direct current voltage, a pair of parallel paths connected to be energized from said source of voltage and each including in series an electric valve having a control member and an impedance element, electric valve means connected in parallel with each of said electric valves and a portion of each of said impedance elements, means including a control circuit for energizing the control members of said electric valve means to effect periodic transfer of current from one of said valve means to the other and thereby effect alternate energization of said impedance elements to provide a periodic voltage, and means for controllin the conductivity of said electric valves to modify the time pattern of said periodic voltage.

2. In combination, a source of direct current voltage, a pair of parallel paths connected to be energized from said source of voltage and each including in series an electric valve having a control member and an impedance element, means including a control circuit for energizing the control members of said electric valves to effect periodic transfer of current from one of said valves to the other and thereby to effect alternate en'- ization of said impedance elements to produce a periodic voltage, a series connected electric valve means and an impedance element connected across each of said electric valves, and means for controlling the conductivity of said electric valve means to produce across said last mentioned impedance element a periodic voltage displaced with respect to said first mentioned periodic voltage.

3. In combination, a source of voltage, a pair of parallel electric paths connected for energizatlon from said source and each including an impedance element connected in series with an electric valve having a control member, means including an energizing circuit for said control members for effecting periodic transfer of current from one of said parallel electric paths to the other to energize alternately said impedance elements and thereb to produce a periodic control voltage across each of said elements, a series connected circuit controlling means and an impedance connected in parallel with each of said electric valves, and means for controlling said circuit controlling means to produce a control voltage across the impedance in parallel with said electric valves having a modified time pattern with respect to said first control voltage in accordance with the operation of said circuit controlling means. i

4. In combination. a source of direct current voltage, means energized from said source for establishing a point of reference potential, 9. pair of parallel paths connected to be energized from said source of voltage and each including in series an electric valve and impedance means, an electric valve means associated with each of said parallel paths and each having the anode-cathode circuit thereof connected in shunt with one of said electric valves and at least a portion of one of said impedance means, means including a control circuit for energizing the control members of said electric valve means to effect periodic transfer of current from one of said valve means to the other and thereby effect alternate energization of said impedance means to provide an output periodic voltage between a point on one of said paths and said point of reference potential, and means for controlling the conductivity of said electric valves to modify said periodic voltage.

5. In combination, a source of direct current voltage, means energized from said source providing a point of reference potential, a pair of parallel paths connected to be energized from said source of voltage and each including in series an electric valve and impedance means. an electric valve means associated with each of said parallel paths and each having the anode-cathode circuit thereof connected in shunt with one of said electric valves and at least a portion of one of said impedance means, means including a control circuit for energizing the control members of said electric valve means to effect periodic transfer of current from one of said valve means to the other and thereby effect alternate encrgization of said impedance means to provide an output periodic voltage between a point on one of said paths and said point of reference potential, and means for controlling the cdnductivity of one of said first mentioned valves to maintain said output voltage after the transfer of current from the electric valve means in the path from which said output voltage i obtained.

6. In combination, a source of voltage, parallel electric paths energized from said source of voltage, an impedance element and an electric valve connected in series in each of said paths, a timing circuit for controlling the conductivities of said electric valves to render said valves alternately conductive and nonconductive at a definite periodicity to produce periodic voltages across the impedance elements of said parallel paths, an electric valve means connected in parallel with each of said electric valves, and means for controlling said electric valve means to render both of said last valve means conductive simultaneously to modify said periodic voltages.

7. In combination, a source of direct current voltage, means energized from said source for establishing a, point of reference potential, 3. pair of parallel paths connected to be energized from said source of voltage and each including in series an electric valve and impedance means, an electric valve means associated with each of said parallel paths and each having the anode-cathode circuit thereof connected in shunt with one of said electric valves and at least a portion of one of said impedance means, means including a control circuit for energizing the control members of said electric valve means to effect periodic transfer of current from one of said valve means to the other and thereby effect alternate energization of said impedance means to provide output periodic voltages between said point of reference potential and a point on each of said parallel paths, means for rendering said electric valves alternately conductive to modify'said eriodic voltage, and means for intermittently rendering said electric valves conductive simultaneously.

8. In combination, a source of direct current voltage, parallel electric paths energized from said source of voltage, an impedance element and an electric valve of the gaseous discharge type connected in series in each of said paths, a timing circuit for controlling the conductivities of said electric valves to render said valves alternately conductive and nonconductive at a definite periodicity to produce'periodic voltages across the impedance elements of said parallel paths, an electric valve of the high vacuum type connected in parallel with each of said electric valves, and means for controlling said high vacuum electric valve means 'to render both of said high vacuum valves conductive simultaneously to modify said periodic voltages.

ORRIN .W. LIVINGSTON. 

